Python Native Datatypes -- list

>>>  li  =  [ " a " ,  " b " ,  " mpilgrim " ,  " z " ,  " example " ]
>>>  li
[ ' a ' ,  ' b ' ,  ' mpilgrim ' ,  ' z ' ,  ' example ' ]
>>>  li[0]
' a '
>>>  li[ 4 ]
' example '

 

1、list的元素是有序的
2、list可以当成数组来用，元素下标从0开始

>>> li
['a', 'b', 'mpilgrim', 'z', 'example']
>>> li[−1]
'example'
>>> li[−3]
'mpilgrim'

 

3、list的索引可以是负数，表达式L[n]的含义为：
（1）当0 <= n <= len(L)-1 时， 跟java、C中的数组元素索引一样
（2）当-len(L) <= n <= -1 时, L[n] = L[len(L)+n]
（3）n不再上述范围内是，程序引发IndexError

li = ['a', 'b', 'String', 'list', 'dictionary']
print li[0:3]
print li[:]
print li[:3]
print li[1:]
print li[0:7] # won't cause IndexError
print li[-2:-1] # identical to li[len(li)-2 : len(li)-1]=li[3:4]
print li[-1:-2] # identical to li[4:3], so it will return a empty list
print li[-125:1159]

 

运行结果：

['a', 'b', 'String']
['a', 'b', 'String', 'list', 'dictionary']
['a', 'b', 'String']
['b', 'String', 'list', 'dictionary']
['a', 'b', 'String', 'list', 'dictionary']
['list']
[]
['a', 'b', 'String', 'list', 'dictionary']

 

4、L[a:b]（其中a,b为整数）表示一个分片操作，注意a，b可以是任意的整数，而且分片操作永远不会引发IndexError。但是a，b取不同的值时，程序行为稍有不同。
（1）当 0 <= a < b < len(L)时，L[a:b]返回一个由L[a], L[a+1]...L[b-1]组成的list
（2）当 0 <= b <= a < len(L)时，L[a:b]返回空的list
（3）当a，b取值不在上述范围时，应用以下4条规则替换a，b的值，得到a，b新的值后再应用上面两条规则。

• 若 a >= len(L), 则 a = len(L)-1
• 若 -len(L) <= a < 0, 则 a = len(L) + a
• 若 a <  -len(L)， 则  a =  0
• b的情况跟a一样
  
• 当 a没有指定时，a = 0, 当b没指定时，b=len(L)-1

5、append和extend方法的不同，看下例就一目了然了。

>>> li = ['a', 'b', 'c']
>>> li.extend(['d', 'e', 'f'])
>>> li
['a', 'b', 'c', 'd', 'e', 'f']
>>> len(li)
6
>>> li[−1]
'f'
>>> li = ['a', 'b', 'c']
>>> li.append(['d', 'e', 'f'])
>>> li
['a', 'b', 'c', ['d', 'e', 'f']]
>>> len(li)
4
>>> li[−1]
['d', 'e', 'f'

 

注意 extend的参数不仅仅可以是list，也可以是一个tuple, dictionary等可以iterable的数据结构
6、

 

List object methods

Method

Description

Nonmutating methods
L .count( x )	Returns the number of items of L that are equal to x .
L .index( x )	Returns the index of the first occurrence of an item in L that is equal to x , or raises an exception if L has no such item.
Mutating methods
L .append(x )	Appends item x to the end of L ; e.g., L [len( L ):]=[ x ] .
L .extend(s )	Appends all the items of iterable s to the end of L ; e.g., L [len( L ):]= s .
L .insert(i, x )	Inserts item x in L before the item at index i , moving following items of L (if any) "rightward" to make space (increases len( L ) by one, does not replace any item, does not raise exceptions: acts just like L [ i : i ]=[ x ] ).
L .remove(x )	Removes from L the first occurrence of an item in L that is equal to x , or raises an exception if L has no such item.
L .pop([i ])	Returns the value of the item at index i and removes it from L ; if i is omitted, removes and returns the last item; raises an exception if L is empty or i is an invalid index in L .
L .reverse( )	Reverses, in place, the items of L .
L .sort([ f ]) (2.3)	Sorts, in place, the items of L , comparing items pairwise via function f ; if f is omitted, comparison is via the built-in function cmp . For more details, see "Sorting a list " on page 57.
L .sort(cmp=cmp, key=None, reverse=False) (2.4)	Sorts, in-place, the items of L , comparing items pairwise via the function passed as cmp (by default, the built-in function cmp ). When argument key is not None , what gets compared for each item x is key ( x ) , not x itself. For more details, see "Sorting a list " on page 57.

7、

>>> li = ['a', 'b', 'mpilgrim']
>>> li = li + ['example', 'new']
>>> li
['a', 'b', 'mpilgrim', 'example', 'new']
>>> li += ['two']
>>> li
['a', 'b', 'mpilgrim', 'example', 'new', 'two']
>>> li = [1, 2] * 3
>>> li
[1, 2, 1, 2, 1, 2]

 

注意下面的例子：

li = ['a']
print li

#li = li + 'b'  TypeError: can only concatenate list (not "str") to list

li += 'b'
print li

li = li * 2                      
print li

li *= 2
print li

 

运行结果：

['a']
['a', 'b']
['a', 'b', 'a', 'b']
['a', 'b', 'a', 'b', 'a', 'b', 'a', 'b']